Recent advances in focused ion beam technology and applications
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Introduction The focused ion beam (FIB) microscope has been widely used for more than two decades, most significantly in the semiconductor industry but also in various materials science and biomaterials fields.1 It generally consists of an ion source, a series of electrostatic lenses to shape the beam, and a scan generator to guide the beam onto a sample with a moving stage. The collision cascade generated by the ion as it interacts with the sample causes sputtering and also generates secondary electrons (SEs) that are gathered by traditional SE detectors. While the contrast attributable to the ion beam is unique, making it sensitive, for example, to phase and grain orientation (see the article by Joy and Michael in this issue), the intuitive image that is formed by an FIB resembles that from a scanning electron microscope (SEM). In addition, the primary energetic ions are much more massive than energetic electrons, providing the ability to sputter material in a site-specific manner that is unique to the FIB. This ability to machine material in a controlled manner with sequential or simultaneous SEM imaging makes the dual platform FIB-SEM a very versatile analytical instrument. The FIB was first used in the late 1980s by the semiconductor industry for mask repair and circuit edit applications.2,3 It achieved widespread use and applications development in the materials and biological sciences when it was coupled with
an SEM column onto a dual platform instrument. An example of dual platform geometry is shown in Figure 1.4 In a typical dual platform instrument, an electron column is mounted vertically, and the ion column is mounted at an oblique angle (∼45° to 55° from the vertical). Column positions are reversed in some dual platform instruments. Figure 1a shows a traditional SEM imaging and energy dispersive x-ray spectrometry (EDS) analysis configuration, while Figure 1b shows a typical FIB milling configuration where the sample surface is normal to the incident ion beam. By placing the sample at a stage height where the electron beam and the ion beam coincide (as shown in Figure 1 beam traces), FIB processing and SEM characterization processes can be co-localized. In fact, this opened the door to site-specific characterization of materials using electron-induced characteristic x-rays, electron backscattered diffraction, and other electron generated signals that are not directly generated by the ion beam (although small but significant numbers of characteristic x-rays are indeed generated5). The most widespread application of the FIB-SEM, and one that hastened its rapid development and commercialization, is for creating site-specific scanning transmission electron microscopy (S/TEM) samples for conventional and higher resolution imaging.6–11 One of the fastest growing application areas for FIB-SEM in recent years is 3D imaging and materials analysis. Until recently,
Nabil Bassim, US Naval Research Laboratory; [email protected] Keana Scott, National Institute of Standards and Technology, Materials Measurement Scie
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